Flotation foam is required in aircraft seat cushions to meet certain FAA flotation requirements in order to serve as a flotation device in the event of an emergency. As illustrated in FIG. 4, conventional bottom cushions 10 on aircraft seats typically include all of their flotation foam formed as a slab 12 that is bonded to the underside of more comfortable open cell foam 14. The open cell foam cushion 14 may also include a layer of structural foam bonded to its underside. The cushion 10 may include additional layers as well, such as adhesives layers, insulating layers and fire blocking layers/coatings. The cushion 10 is typically covered with durable upholstery for aesthetic purposes and to protect the underlying foam.
The foam slab 12 is typically constructed from closed cell foam, such as polyethylene, and has a thickness of about a few centimeters. Because the closed cell foam is relatively rigid, it is typically positioned away from the passenger to prevent discomfort. The open cell foam 14 is typically constructed from polyurethane for softness and comfort, and has a thickness significantly greater than that of the flotation foam slab 14 for providing comfort and preventing contact with the underlying flotation foam. Although the open cell foam thickness is typically sufficient for comfort for lightweight passengers and short flight times, heavier passengers and longer flights can cause the comfort foam to compress to the point that hard points are felt by the passenger. Although one solution to the compression problem may be to simply increase the thickness of the comfort foam, this solution is not practical or possible given seat designs and space constraints of typical seat installations.
The structural foam is also necessary to reduce the load on the occupant's lumbar region during an emergency landing scenario. The FAA requires a 14 g crash test to simulate such as event, in which all parts of the seat must remain intact. Compressive load to the occupant's lumbar region must also be minimized. The structural foam decelerates the occupant so that when the occupant strikes the metal or composite structure below the foam, the impulse load is less than if no structural foam was present.
In addition to compression problems, rigid closed cell foam slabs are substantially impenetrable to air and moisture, and thus form a barrier that prevents air and moisture from passing through the cushion for drying and wicking away moisture. While the seat upholstery is intended to be substantially water-resistant, moisture may still seep through the upholstery and the seams. The underlying open cell foam acts much like a sponge in absorbing water, and absorbed moisture increases the weight of the seat, affects the performance of the cushion, causes the foam to deteriorate, and makes the seat uncomfortable.
Accordingly, there is a need for improved seat cushion construction that increases seat performance, reduces seating discomfort associated with conventional flotation foam slabs, and improves the breathability of the seat cushion.